This invention relates to field emission transistors.
Numerous field emission devices have been known in the art. Examples of such prior art include U.S. Pat. Nos. 4,578,614; 5,469,015; 5,739,628; and 5,955,833. Such devices are generally made with semiconductor micro-fabrication techniques, and include an emitter with a sharp point or edge to concentrate the applied electric fields to greater than 109 volts/meter in order to stimulate field emission of electrons. Also included in such devices is a gate or grid spaced between the emitter and a collector. Such gates either restrict or enhance the electric field at the tip of the emitter in order to diminish or augment electron emission from said emitter toward said collector.
Field emission devices are capable of extremely fast switching speeds, small sizes, and high operating temperatures, however prior art devices have been unable to come to significant commercial success due to a number of problems.
Such prior art devices are created with difficult fabrication techniques, and experience a variety of functional weaknesses. Such functional weaknesses include high operational voltages, poor switching characteristics, and the inability of such devices to be easily integrated together into usable circuits.
The above mentioned prior art necessarily has high operational voltage requirements because of the need to have the gate positioned between the emitter and the collector, and the fact that they cannot be made in complimentary pairs to enhance the field of each device. As the electric field density is proportional to distance, the greater distance between the emitter and the collector necessitates a higher applied voltage to get the required 109 volts/meter at the emitter tip.
U.S. Pat. No. 5,461,280 teaches that a photon source impinging upon the emitter can lower the required applied voltage, but said patent teachings still have the inherent problem of the gate positioned between the emitter and the collector, which keeps the operational voltage high.
Said gate positioning also creates a number of functional weaknesses with the prior art. With said gate between the emitter and the collector, prior art devices behave similar to triode vacuum tubes. In such prior art devices, if the voltage between the collector and the emitter is sufficient to induce field emission, then the gate must be connected to a voltage source lower than the emitter voltage to turn the device off. If the collector to emitter voltage is not sufficient to induce emission, then a positive voltage applied to the gate can cause emission to begin. However, such a positive voltage will create a gate current, and unwanted effect, which will increase as the positive potential on the gate increases. In the case that the voltage potential of the gate is near to that of the collector, the undesired gate current can be much higher than the desired collector-emitter current. These undesirable characteristics make it difficult to have one prior art device drive another, as the required gate input voltages are different from the device output voltages.
Another functional problem with the prior art is that such devices cannot be made into complimentary pair configurations where one of the devices will turn on with an applied high voltage, while the other turns on with an applied low voltage. Complimentary pairs are very valuable in making integrated circuits that are simple, fast, and consume low amounts of power.
With their fabrication difficulties, gate voltage requirements, high operational voltage, and their inability to be made in complimentary pairs, prior art devices are not easily integrated together into practical circuits.
Accordingly there exists a need for field emission devices that can be easily integrated together into practical circuitry.
The present invention has been developed in order to overcome the above-mentioned weaknesses that are inherent in the prior art, and to provide a variety of switching devices that can be easily utilized by the electronics industry.
The present invention is a field emission transistor which is easily fabricated in a planar fashion by modern semiconductor fabrication technology. Said invention regulates the collector-emitter current by means of insulated gates that are not between the emitter and collector. A gate near the collector produces an N type transistor, which turns on with the application of a high signal.
The insulated gate regulates the collector-emitter current by changing the field intensity between the collector and the emitter. The close proximity of the collector to the emitter, as well as the application of photons to the emitter, result in very low operational voltages.
In another embodiment, the insulated gate is placed near the emitter, creating a P type transistor, which turns on by the application of a low signal.
In a further embodiment, both P type and N type transistors are integrated together into a complimentary pair that has a single gate, and has enhanced on-state characteristics.
In still another embodiment, the P and N type transistors are integrated together to form NAND gates and NOR gates, the building blocks for digital logic circuits.